Phased array has emerged as a rapid imaging technique in bio-medical and non-destructive evaluation applications, where ultrasonic waves are used for imaging. Other applications in the field of Radar imaging, Ground penetrating Radar (GPR) imaging, etc. can be found where microwaves are employed for imaging. This phased array method is preferred over conventional single transducer method is due to its flexibility in varying the angle of interrogation and/or focusing of the wave field to the point of interest through electronic means reducing the need to move the probe physically and at the same time increasing the imaging volume.
Since the phased array is based on the superposition of waves, the depth to which inspection is possible is directly related to the aperture size (and consequently the near field) of the phased array transducer. In the case of interrogation of thick materials, this limitation is a handicap. Increasing the number of active elements of the phased array system significantly adds additional complexity and cost in the electronic part of the system.
Other deficiencies of the current phased array focusing methods are (a) the focusing quality decreases with increase in the angle of orientation of the beam, (b) in case of complex geometries, there is no provision for any optimisation based on the geometries, (c) the current imaging uses only longitudinal ultrasonic waves in the case of imaging using ultrasonics in materials (d) the current phased array imaging techniques have limited compensation for material anisotropy and inhomogenity, (e) the current phased array imaging methods have limited applications when the surface contours of the material being interrogated is non-uniform.